1. Field of the Invention
The invention relates to an electronic interface for a telephone set comprising an integrated circuit. In particular, it relates to an integrated circuit which performs the majority of modulation functions in the set on signals transmitted over the telephone line.
2. Description of the Prior Art
This type of integrated circuit is generally provided in one diagonal of a rectifier bridge to whose other diagonal the telephone line is connected. It has at least two terminals, a modulated signal terminal and a reference terminal, respectively.
Examples of such interfaces are disclosed in application diagrams published with the specifications of the integrated circuits TEA 1046 or TEA 1060, in the form of special instalments, or in the handbook "Components for telephony" published by the firm of PHILIPS.
However, certain standards relating to telephones require the current consumed by the line when the set is in the off-hook condition to be limited, and these standards are not fully taken into account in the above-mentioned application diagrams. They disclose an arrangement formed by a first field-effect transistor in series with a current measuring resistor between the integrated circuit and the rectifier bridge, and a second transistor whose emitter-base junction is in parallel with the current measuring resistor, the collector being connected to the control electrode of the first transistor. This basic arrangement satisfies however only part of the requirements of the standards. It has therefore been necessary to provide a plurality of additional circuits, each satisfying a specific requirement of the standards.